Field of the Invention
This invention relates generally to a sandwich structure including a non-conducting core that is employed to weld different metal structures together and, more particularly, to a method for welding different vehicle metal panels together using a sandwich structure having a non-conducting core so as to eliminate galvanic corrosion between the panels.
Discussion of the Related Art
A typical vehicle will include a configuration of structural support members, sometimes referred to as a vehicle frame or chassis, that are secured together in a desired configuration using suitable bolts, welds, adhesives, etc. In order to provide a desired combination of style, strength and weight of the vehicle, these structural elements are often made of different metals, such as aluminum and steel. When different electrically conductive metal components are secured together by welds, bolts, etc., galvanic corrosion sometimes occurs at the interface between the different metals, which reduces the integrity of the material at the joint over time. Various procedures are known in the art to reduce galvanic corrosion between two dissimilar metals, such as by providing a non-electrical barrier or coating on the metal structural elements, for example, providing anodized aluminum. Although these known techniques for reducing or eliminating galvanic corrosion have been generally successful, improvements can still be made.
It is known in the art to provide vehicle structural members having sandwich structures. These structural members can generally be categorized into three designs, namely, hollow beams that are fully or partially reinforced with a polymer or metallic foam, single or dual-sided facesheets reinforced with a honeycomb-like cellular core, and formed composite structural member. For hollow metallic or polymer matrix composite tube structures, which are fully or partially reinforced with a lightweight foam core, the material used for the core can be either a metallic or polymeric foam that is bonded, mechanically attached or interference fit into the tube structure. The purpose of the core is to carry shear loads in the sandwich structures and absorb energy in the event of a low or high speed impact, which is a distinction dependent on the density and composition of the foam. The use of honeycomb or honeycomb-like ordered cellular cores to provide reinforcement to one or two flat facesheets have an open-sided sandwich designs and have honeycomb, discrete-stiffened or wine-crate structures extending from the front face of the structural member back towards the passenger compartment of the vehicle.
It is also known in the art to fabricate a three-dimensional network of photopolymer waveguides comprising a unitary truss or lattice architecture, hereafter referred generally as a micro-truss structure or micro-truss core. For example, U.S. Pat. Nos. 7,653,279 and 7,382,959 disclose a process for fabricating such a micro-truss structure. Generally, the process includes providing a reservoir or mold filled with a volume of a curable monomer and covered by a mask including strategically positioned apertures. UV light sources are positioned relative to the mask and exposure to collimated UV light through the mask apertures forms a series of interconnected self-propagating photopolymer waveguides, referred to herein as struts, to form the truss or lattice architecture. Once the photopolymer waveguides are formed, the reservoir is emptied of the unpolymerized monomer which was not exposed to UV light. The micro-truss structure may then undergo a post-cure operation to increase the cross-link density in the photopolymer waveguides. This post-cure may be accomplished via a thermal cure, an additional exposure to UV light, an equivalent method or combinations thereof.